This Phase I, multicenter, randomized, placebo-controlled, double-blind trial will evaluate the safety and immunogenicity of the prime-boost immunization approach in vaccinia-naive and vaccinia-immune individuals using a novel recombinant vaccine vector expressing HIV-1 envelope, and poly gene products and subsequently will address questions pertaining to the optimal boosting strategy raised by the previous trials of vaccinia recombinant expressing gp160 alone. We continue to recruit subjects for this study.